SEATTLE — Bill Gates and Warren Buffett, America's two richest people, are embarking on a campaign to persuade their super-rich peers to give half their fortunes to charity in a move that could change the face of philanthropy.

The effort, if successful, could funnel a colossal amount of money into nonprofit groups. If the individuals on the Forbes 400 list of richest Americans pledged half their net worth to charity, that would amount to $600 billion, Fortune magazine says.

Fortune, in an article posted Wednesday, detailed the origin and status of the campaign, which it called "the biggest fundraising drive in history."

Several of the megarich, including Los Angeles philanthropists Eli and Edythe Broad; Silicon Valley's John and Tashia Morgridge, whose fortune came from Cisco Systems; venture capitalist John Doerr of Kleiner Perkins and his wife, Ann; and media entrepreneur Gerry Lenfest and his wife, Marguerite, have already committed to the 50 percent pledge, according to program organizers. Buffett and Bill and Melinda Gates are sending e-mails and making calls to other billionaires deemed likely prospects to contribute, Fortune reported.

Buffett said it's a good bet the super-wealthy have already thought about what to do with their money. "They may not have reached a decision about that, but they have for sure thought about it. The pledge that we're asking them to make will put them to thinking about the whole issue again," the Berkshire Hathaway chairman told Fortune.

"If they wait until they're making a final will in their 90s, the chance of their brainpower and willpower being better than they are today is nil."

First supperThe campaign began just over a year ago, when Gates and Buffett — who represent a combined net worth of $90 billion, according to Forbes — invited several billionaires to
a secret dinner meeting
in New York. Among those attending were Hungarian-born hedge fund guru George Soros, talk-show host Oprah Winfrey, David Rockefeller, media mogul Ted Turner and New York City Mayor Michael Bloomberg.

Rockefeller, of the oil tycoon family, was asked to host the exploratory meeting at the exclusive President'sHouse at Rockefeller University. Rockefeller, now 95, told Fortune that the request was "a surprise but a pleasure."

Melinda Gates insisted that both husbands and wives be invited. Her reasoning, according to Fortune: "Even if he's the one that made the money, she's going to be a real gatekeeper. And she's got to go along with any philanthropic plan, because it affects her and it affects their kids."

According to media reports at the time, each attendee was given 15 minutes to speak about how they saw the future global economic climate, the future priorities for philanthropy, and what they felt the elite group should do.

A second and third dinner followed in the months to come — at the New York Public Library and at the Rosewood Sand Hill hotel in Menlo Park, Calif.

At those dinners, Bill Gates, the Microsoft co-founder, told Fortune, "No one ever said to me, 'We gave more than we should have.'"

Billionaire pledgeThe principals eventually settled on a goal of 50 percent of net worth, though Buffett himself is pledging 99 percent. They set up a website, givingpledge.org, about the effort.

"Millions of people who regularly contribute to churches, schools and other organizations thereby relinquish the use of funds that would otherwise benefit their own families," Buffett wrote in a statement on the website explaining his pledge. "The dollars these people drop into a collection plate or give to United Way mean forgone movies, dinners out, or other personal pleasures. In contrast, my family and I will give up nothing we need or want by fulfilling this 99 percent pledge."

"The Pledge is a moral commitment to give, not a legal contract. It does not involve pooling money or supporting a particular set of causes or organizations," the website says.

"While the Giving Pledge is specifically focused on billionaires, the idea takes its inspiration from efforts in the past and at present that encourage and recognize givers of all financial means and backgrounds. We are inspired by the example set by millions of Americans who give generously (and often at great personal sacrifice) to make the world a better place."

The giving pledge focuses for now on American billionaires, but the effort may eventually extend worldwide.

The money from the participating billionaires isn't being collected or distributed; rather, the pledge is a commitment to give.

Melinda Gates says the initial goal of the pledge campaign is to get billionaires moving in the direction of giving.

"Three to five years down the road, we need to have a significant number of billionaires signed up. That would be success," she told Fortune.